高手赐教, gdw-8-29

monstercn

gdw-8-29

The annual rent collected by a corporation from a certain building was x percent more in 1998 than in 1997 and y percent less in 1999 than in 1998.  Was the annual rent collected by the corporation from the building more in 1999 than in 1997?

(1)     x > y

(2)   xy/100 < x – y

答案选b，实在证明不出来，高手亲赐教，谢谢

monstercn

ziding !

strawdog

以下是引用monstercn在2008-9-26 13:03:00的发言：

gdw-8-29

The annual rent collected by a corporation from a certain building was x percent more in 1998 than in 1997 and y percent less in 1999 than in 1998.  Was the annual rent collected by the corporation from the building more in 1999 than in 1997?

(1)     x > y

(2)   xy/100 < x – y

答案选b，实在证明不出来，高手亲赐教，谢谢

assuming annual rent for 1997 is R, then in 1998, the annual rent is R(1+x%), and annual rent for 1999 is R(1+x%)(1-y%)

比较R(1+x%)(1-y%)和R的大小，就是要比较(1+x%)(1-y%)和1的大小

(1+x%)(1-y%)-1=x%-y%-x%y%=[(x-y)-xy/100]/100，当满足条件2的时候，我们就可以得出1999的rent比1997高